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[109.81.31.43]) by smtp.gmail.com with UTF8SMTPSA id a640c23a62f3a-b0783047123sm182588966b.14.2025.09.10.08.15.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 10 Sep 2025 08:15:16 -0700 (PDT) Date: Wed, 10 Sep 2025 17:15:14 +0200 From: Michal Hocko To: zhongjinji Cc: rientjes@google.com, shakeel.butt@linux.dev, akpm@linux-foundation.org, tglx@linutronix.de, liam.howlett@oracle.com, lorenzo.stoakes@oracle.com, surenb@google.com, lenb@kernel.org, rafael@kernel.org, pavel@kernel.org, linux-mm@kvack.org, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, liulu.liu@honor.com, feng.han@honor.com Subject: Re: [PATCH v9 1/2] mm/oom_kill: Thaw the entire OOM victim process Message-ID: References: <20250910143726.19905-1-zhongjinji@honor.com> <20250910143726.19905-2-zhongjinji@honor.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250910143726.19905-2-zhongjinji@honor.com> On Wed 10-09-25 22:37:25, zhongjinji wrote: > OOM killer is a mechanism that selects and kills processes when the system > runs out of memory to reclaim resources and keep the system stable. But the > oom victim cannot terminate on its own when it is frozen, even if the OOM > victim task is thawed through __thaw_task(). This is because __thaw_task() can > only thaw a single OOM victim thread, and cannot thaw the entire OOM victim > process. > > Also, freezing_slow_path() decides whether a task is an OOM victim by checking > the task's TIF_MEMDIE flag. When a task is thawed, the freezer bypasses PM > freezing and cgroup freezing states to thaw it. But TIF_MEMDIE is not a thread > group shared flag, and only one thread is marked with TIF_MEMDIE. If other > threads are thawed, they may still remain frozen due to PM freezing and cgroup > freezing states. > > To solve this, thaw_process() is introduced to thaw all threads of the victim, > ensuring every thread in the victim process can be thawed. The freezer uses > tsk_is_oom_victim() to determine whether a task is an OOM victim, because > tsk->signal->oom_mm is data shared by all threads. This allows all victim threads > to rely on it to be thawed. A history detour for future reference. TIF_MEMDIE was a "this is the oom victim & it has access to memory reserves" flag in the past. It has that thread vs. process problems and tsk_is_oom_victim was introduced later to get rid of them and other issues as well as the guarantee that we can identify the oom victim's mm reliably for other oom_reaper. I recommend reading git log of mm/oom_kill.c to get hairy history of that area and how tricky it is due all the subtle interaction with process exit paths etc. > > This change will thaw the entire victim process when OOM occurs, > ensuring that the oom victim can terminate on its own. > > Signed-off-by: zhongjinji Acked-by: Michal Hocko Thanks! > > Acked-by: Michal Hocko > --- > include/linux/freezer.h | 2 ++ > kernel/freezer.c | 20 +++++++++++++++++++- > mm/oom_kill.c | 10 +++++----- > 3 files changed, 26 insertions(+), 6 deletions(-) > > diff --git a/include/linux/freezer.h b/include/linux/freezer.h > index b303472255be..32884c9721e5 100644 > --- a/include/linux/freezer.h > +++ b/include/linux/freezer.h > @@ -47,6 +47,7 @@ extern int freeze_processes(void); > extern int freeze_kernel_threads(void); > extern void thaw_processes(void); > extern void thaw_kernel_threads(void); > +extern void thaw_process(struct task_struct *p); > > static inline bool try_to_freeze(void) > { > @@ -80,6 +81,7 @@ static inline int freeze_processes(void) { return -ENOSYS; } > static inline int freeze_kernel_threads(void) { return -ENOSYS; } > static inline void thaw_processes(void) {} > static inline void thaw_kernel_threads(void) {} > +static inline void thaw_process(struct task_struct *p) {} > > static inline bool try_to_freeze(void) { return false; } > > diff --git a/kernel/freezer.c b/kernel/freezer.c > index 6a96149aede9..ddc11a8bd2ea 100644 > --- a/kernel/freezer.c > +++ b/kernel/freezer.c > @@ -10,6 +10,7 @@ > #include > #include > #include > +#include > #include > > /* total number of freezing conditions in effect */ > @@ -40,7 +41,7 @@ bool freezing_slow_path(struct task_struct *p) > if (p->flags & (PF_NOFREEZE | PF_SUSPEND_TASK)) > return false; > > - if (test_tsk_thread_flag(p, TIF_MEMDIE)) > + if (tsk_is_oom_victim(p)) > return false; > > if (pm_nosig_freezing || cgroup_freezing(p)) > @@ -206,6 +207,23 @@ void __thaw_task(struct task_struct *p) > wake_up_state(p, TASK_FROZEN); > } > > +/* > + * thaw_process - Thaw a frozen process > + * @p: the process to be thawed > + * > + * Iterate over all threads of @p and call __thaw_task() on each. > + */ > +void thaw_process(struct task_struct *p) > +{ > + struct task_struct *t; > + > + rcu_read_lock(); > + for_each_thread(p, t) { > + __thaw_task(t); > + } > + rcu_read_unlock(); > +} > + > /** > * set_freezable - make %current freezable > * > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > index 25923cfec9c6..88356b66cc35 100644 > --- a/mm/oom_kill.c > +++ b/mm/oom_kill.c > @@ -772,12 +772,12 @@ static void mark_oom_victim(struct task_struct *tsk) > mmgrab(tsk->signal->oom_mm); > > /* > - * Make sure that the task is woken up from uninterruptible sleep > - * if it is frozen because OOM killer wouldn't be able to free > - * any memory and livelock. freezing_slow_path will tell the freezer > - * that TIF_MEMDIE tasks should be ignored. > + * Make sure that the process is woken up from uninterruptible sleep > + * if it is frozen because OOM killer wouldn't be able to free any > + * memory and livelock. The freezer will thaw the tasks that are OOM > + * victims regardless of the PM freezing and cgroup freezing states. > */ > - __thaw_task(tsk); > + thaw_process(tsk); > atomic_inc(&oom_victims); > cred = get_task_cred(tsk); > trace_mark_victim(tsk, cred->uid.val); > -- > 2.17.1 -- Michal Hocko SUSE Labs